Systems and methods for multiple-beam laser arrangements with variable beam parameter product

ABSTRACT

In various embodiments, a beam-parameter adjustment system and focusing system alters a spatial power distribution of a plurality of radiation beams before the beams are coupled into an optical fiber.

RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 61/944,989, filed Feb. 26, 2014, and U.S.Provisional Patent Application No. 61/986,237, filed Apr. 30, 2014, theentire disclosure of each of which is hereby incorporated herein byreference.

TECHNICAL FIELD

In various embodiments, the present invention relates to laser systems,specifically laser systems with controllable beam parameter products.

BACKGROUND

High-power laser systems are utilized for a host of differentapplications, such as welding, cutting, drilling, and materialsprocessing. Such laser systems typically include a laser emitter, thelaser light from which is coupled into an optical fiber (or simply a“fiber”), and an optical system that focuses the laser light from thefiber onto the workpiece to be processed. The optical system istypically engineered to produce the highest-quality laser beam, or,equivalently, the beam with the lowest beam parameter product (BPP). TheBPP is the product of the laser beam's divergence angle (half-angle) andthe radius of the beam at its narrowest point (i.e., the beam waist, theminimum spot size). The BPP quantifies the quality of the laser beam andhow well it can be focused to a small spot, and is typically expressedin units of millimeter-milliradians (mm-mrad). A Gaussian beam has thelowest possible BPP, given by the wavelength of the laser light dividedby pi. The ratio of the BPP of an actual beam to that of an idealGaussian beam at the same wavelength is denoted M², which is awavelength-independent measure of beam quality.

In many laser-processing applications, the desired beam spot size,divergence, and beam quality may vary depending on, for example, thetype of processing and/or the type of material being processed. In orderto make such changes to the BPP of the laser system, frequently theoutput optical system or the optical fiber must be swapped out withother components and/or realigned, a time-consuming and expensiveprocess that may even lead to inadvertent damage of the fragile opticalcomponents of the laser system. Thus, there is a need for alternativetechniques for varying the BPP of a laser system that do not involvesuch adjustments to the laser beam or optical system at the output ofthe optical fiber.

SUMMARY

Various embodiments of the present invention provide laser systems inwhich the BPP of the system (i.e., of its output laser beam) is variedvia manipulation of one or more input laser beams that are coupled intoan optical fiber, rather than via manipulation of the output beam thatexits the fiber. This output beam with controllably variable BPP may beutilized to process a workpiece in such applications as welding,cutting, drilling, etc. Embodiments of the invention vary the focus spotand/or the beam quality of the input laser beam(s) in order to enable acontrollably variable BPP at the output of the laser system. (Referencesherein to an input laser beam are understood to mean “one or more inputlaser beams,” i.e., including the possibility of multiple input laserbeams, unless otherwise indicated.) For example, the focus spot of aninput laser beam may be varied with the input beam having a fixed beamquality, or the beam quality (e.g., beam divergence, beam size, and/orpower) of an input beam may be varied, or a combination of suchtechniques may be utilized.

Embodiments of the present invention couple the one or more input laserbeams into an optical fiber. In various embodiments, the optical fiberhas multiple cladding layers surrounding a single core, multiplediscrete core regions (or “cores”) within a single cladding layer, ormultiple cores surrounded by multiple cladding layers.

Herein, “optical elements” may refer to any of lenses, mirrors, prisms,gratings, and the like, which redirect, reflect, bend, or in any othermanner optically manipulate electromagnetic radiation. Herein, beamemitters, emitters, or laser emitters, or lasers include anyelectromagnetic beam-generating device such as semiconductor elements,which generate an electromagnetic beam, but may or may not beself-resonating. These also include fiber lasers, disk lasers, non-solidstate lasers, etc. Generally, each emitter includes a back reflectivesurface, at least one optical gain medium, and a front reflectivesurface. The optical gain medium increases the gain of electromagneticradiation that is not limited to any particular portion of theelectromagnetic spectrum, but that may be visible, infrared, and/orultraviolet light. An emitter may include or consist essentially ofmultiple beam emitters such as a diode bar configured to emit multiplebeams. The input beams received in the embodiments herein may besingle-wavelength or multi-wavelength beams combined using varioustechniques known in the art.

Embodiments of the invention may be utilized with wavelength beamcombining (WBC) systems that include a plurality of emitters, such asone or more diode bars, that are combined using a dispersive element toform a multi-wavelength beam. Each emitter in the WBC systemindividually resonates, and is stabilized through wavelength-specificfeedback from a common partially reflecting output coupler that isfiltered by the dispersive element along a beam-combining dimension.Exemplary WBC systems are detailed in U.S. Pat. No. 6,192,062, filed onFeb. 4, 2000, U.S. Pat. No. 6,208,679, filed on Sep. 8, 1998, U.S. Pat.No. 8,670,180, filed on Aug. 25, 2011, and U.S. Pat. No. 8,559,107,filed on Mar. 7, 2011, the entire disclosure of each of which isincorporated by reference herein.

In an aspect, embodiments of the invention feature a beam-parameteradjustment system and focusing system for receiving and altering aspatial distribution of a plurality of radiation beams from a pluralityof beam sources and focusing the radiation with the altered spatialdistribution onto an end face of an optical fiber. The spatialdistribution and the altered spatial distribution may be spatial powerdistributions. The radiation beams each have a polarization state andcollectively have a spatial distribution (e.g., a spatial powerdistribution). The system includes or consists essentially of a firstoptical element for splitting each of the radiation beams into aplurality of spatially displaced output beams, the splitting being basedon the polarization states, focusing optics (e.g., one or more lenses,mirrors, and/or other optical elements) for combining the output beamsonto the optical-fiber end face, and a second optical element foraltering a polarization state of (i) at least one of the radiation beamsand/or (ii) at least one of each plurality of output beams prior tocombination thereof by the focusing optics, whereby the combined outputbeams have an output spatial distribution different from the spatialdistribution of the radiation beams, the output distribution beingdetermined by the polarization-based splitting.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The second optical element may includeor consist essentially of a half-wave plate. The first optical elementmay include or consist essentially of a polarizing beam splitter forsplitting the radiation beams into the output beams in accordance withthe polarization states of the radiation beams. The half-wave plate maybe optically upstream of the polarizing beam splitter (i.e., positionedsuch that incoming light strikes the half-wave plate before thepolarizing beam splitter). The polarizing beam splitter may have a topreflective surface angled so that the output beams propagate at anoff-parallel angle relative to optical paths of the radiation beams. Apolarization randomizer for randomizing polarization states of theoutput beams may be optically upstream of the focusing optics. Thepolarization randomizer may include or consist essentially of aquarter-wave plate and/or a polarization scrambler. The first opticalelement may include or consist essentially of a birefringent beamdisplacer for spatially displacing at least some of the radiation beamsbased on the polarization states thereof. The beam displacer may bebirefringent (e.g., uniaxially birefringent), whereby each of theradiation beams is split into an ordinary beam propagating along anoptical axis of the beam displacer and an extraordinary beam propagatingaway from the optical axis. The power distribution between each of theordinary and extraordinary beams may depend on polarization componentsof the corresponding radiation beam. The beam displacer may be wedged sothat the output beams propagate at an off-parallel angle relative tooptical paths of the radiation beams.

The first optical element may include or consist essentially of firstand second polarizing beam splitters. The second optical element mayinclude or consist essentially of a half-wave plate disposed between thefirst and second polarizing beam splitters along an optical axisthereof. The first polarizing beam splitter may split the radiationbeams into a plurality of spatially displaced intermediate beams inaccordance with the polarization states of the radiation beams. Some butnot all of the intermediate beams may propagate along the optical pathsof the radiation beams, and some of the intermediate beams may propagateparallel to but spatially displaced from the optical paths of theradiation beams. The second optical element may intercept and alterpolarization states of at least some of the displaced intermediatebeams. The second polarizing beam splitter may combine at least some ofthe displaced intermediate beams with the intermediate beams that havenot been displaced based on the altered polarization states of thedisplaced intermediate beams intercepted by the second optical element.The system may include a quarter-wave plate, optically upstream of thefirst polarizing beam splitter, for establishing the polarization statesof the radiation beams. A rotation angle of the half-wave plate about anoptical axis thereof may determine an allocation of beam power between amaximum numerical aperture of the radiation beams and a minimumnumerical aperture of the radiation beams.

The first optical element may include or consist essentially of firstand second birefringent beam displacers. The second optical element mayinclude or consist essentially of a half-wave plate disposed between thefirst and second beam displacers along an optical axis thereof. Thefirst beam displacer may displace each of the radiation beams into anordinary intermediate beam propagating along an optical axis of the beamdisplacer and an extraordinary intermediate beam propagating away fromthe optical axis based on the polarization states of the radiationbeams. The second optical element may intercept and alter polarizationstates of the intermediate beams. The second beam displacer may displacethe intermediate beams based on the altered polarization states thereof.The system may include a quarter-wave plate, optically upstream of thefirst polarizing beam splitter, for establishing the polarization statesof the radiation beams.

The first optical element may include or consist essentially of firstand second spaced-apart, substantially optically transparent plates. Theplates may be oriented parallel to each other but angled with respect tooptical paths of the radiation beams. The second optical element mayinclude or consist essentially of a half-wave plate intervening betweenthe first and second plates. Each of the first and second plates mayhave a birefringent surface facing the second optical element and ahighly reflective surface opposite the birefringent surface. Therotation angle of the half-wave plate about an optical axis thereof maydetermine an allocation of beam power between a maximum numericalaperture of the radiation beams and a minimum numerical aperture of theradiation beams.

The first optical element may include or consist essentially of at leastone reflector and first and second spaced-apart, substantially opticallytransparent plates. The plates may be oriented at opposite angles withrespect to optical paths of the radiation beams. The second opticalelement may include or consist essentially of a half-wave plate. Each ofthe first and second plates may have a birefringent surface facing thesecond optical element and a highly reflective surface opposite thebirefringent surface. The first and second plates may be disposed alongthe optical paths of the radiation beams. The reflector may be spacedapart from the optical paths of the radiation beams. The half-wave platemay be disposed between the first plate and the reflector. The first andsecond optical elements may be arranged such that intermediate beamsfrom the first plate travel through the half-wave plate and arereflected by the reflector to the second plate from which they propagatethrough the focusing optics. The first and second plates may be disposedalong the optical paths of the radiation beams. The first and secondreflectors may be spaced apart from the optical paths of the radiationbeams and oriented at opposite angles with respect to each other. Thehalf-wave plate may be disposed between the reflectors. The first andsecond optical elements may be arranged such that intermediate beamsfrom the first plate are directed through the half-wave plate by thefirst reflector and to the second plate by the second reflector so as topropagate through the focusing optics.

In another aspect, embodiments of the invention feature a beam-parameteradjustment system and focusing system for receiving and altering aspatial distribution of a plurality of radiation beams from a pluralityof beam sources and focusing the radiation with the altered spatialdistribution onto an end face of an optical fiber. The spatialdistribution and the altered spatial distribution may be spatial powerdistributions. The system includes or consists essentially of adeformable mirror, focusing optics, and a controller. The deformablemirror has a reflective surface, and the controller alters aconformation (e.g., shape) of the reflective surface. The deformablemirror and the focusing optics are arranged such that the deformablemirror receives the radiation beams and directs them through thefocusing optics onto the end face. The controller is responsive to atarget radiation power distribution and configured to produce a mirrorconformation causing the radiation beams to strike the end face with thetarget radiation power distribution.

In yet another aspect, embodiments of the invention feature abeam-parameter adjustment system and focusing system for receiving andaltering a spatial power distribution of a radiation beam from a beamsource and focusing the radiation with the altered spatial powerdistribution onto an end face of an optical fiber. The system includesor consists essentially of a gradient-index lens having a refractiveindex constant through an optical axis of the lens but varying indirections perpendicular to the optical axis, means for introducing adistortion in the lens to vary a waist, spot size, beam quality, entryangle (into the fiber), and/or divergence of a beam emerging from thelens, and a controller for controlling the distortion-introducing meansto achieve a target altered spatial power distribution on the end face.The distortion-introducing means may be at least one of a local heater,a radiation source directed into the lens, an acousto-optic modulatorand/or transducer altering an optical property of the lens, or anelectro-optic modulator and/or transducer altering an optical propertyof the lens. The reflective surface may have a controllable phase error,the phase error producing the target radiation power distribution.

In another aspect, embodiments of the invention feature a beam-parameteradjustment system and focusing system for receiving and altering aspatial power distribution of a radiation beam from a beam source andfocusing the radiation with the altered spatial power distribution ontoan end face of an optical fiber. The system includes or consistsessentially of focusing optics, a heating source for introducing aheat-dependent distortion in the focusing optics to vary a waist, spotsize, beam quality, entry angle (into the fiber), and/or divergence of abeam emerging therefrom, and a controller for controlling the heatingsource to achieve a target altered spatial power distribution on the endface.

In yet another aspect, embodiments of the invention feature abeam-parameter adjustment system and focusing system for receiving andaltering a spatial power distribution of a radiation beam from a beamsource and focusing the radiation with the altered spatial powerdistribution onto an end face of an optical fiber. The system includesor consists essentially of a focusing optics, a fiber end cap opticallycoupling radiation from the focusing optics into the fiber end face (andwhich may be butt-coupled, e.g., gaplessly butt-coupled, to the fiberend face), means for introducing a distortion in the fiber end cap tovary a waist, spot size, beam quality, entry angle (into the fiber),and/or divergence of a beam emerging from the focusing optics (and/orthe end cap), and a controller for controlling thedistortion-introducing means to achieve a target altered spatial powerdistribution on the end face. The distortion-introducing means mayinclude or consist essentially of at least one of a local heater, aradiation source directed into the end cap, an acousto-optic modulatorand/or transducer altering an optical property of the end cap, or anelectro-optic modulator and/or transducer altering an optical propertyof the end cap.

In another aspect, embodiments of the invention feature a beam-parameteradjustment system and focusing system for receiving a radiation beamfrom a beam source and focusing the radiation onto an end face of anoptical fiber. The system may include or consist essentially of focusingoptics and a segment of gradient-index fiber for optically couplingradiation from the focusing optics into the fiber end face with analtered spatial power distribution. The segment of gradient-index fibermay be butt-coupled to the end face.

In yet another aspect, embodiments of the invention feature abeam-parameter adjustment system and focusing system for altering aspatial power distribution of a plurality of radiation beams. The systemmay include or consist essentially of a plurality of beam sources foremitting radiation beams (e.g., laser beams), focusing optics (e.g., atleast one focusing lens) for focusing radiation from the beam sourcesonto the end face of an optical fiber, and a beam pathway adjuster forshifting the beams to achieve a target spatial power distribution on theend face. The beam pathway adjuster may alter a spacing between thebeams from the beam sources to achieve the target spatial powerdistribution. The beam pathway adjuster may shift at least some of thebeams relative to the focusing optics to achieve the target spatialpower distribution. The system may include means for selectivelyaltering a power of at least one of the beams (e.g., a controller formodulating power into and/or out of at least one beam emitter) toachieve the target spatial power distribution.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, the term“substantially” means ±10%, and in some embodiments, ±5%. The term“consists essentially of” means excluding other materials thatcontribute to function, unless otherwise defined herein. Nonetheless,such other materials may be present, collectively or individually, intrace amounts. Herein, the terms “radiation” and “light” are utilizedinterchangeably unless otherwise indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 is a schematic diagram of a laser system in accordance withvarious embodiments of the invention;

FIGS. 2A-2C are schematic diagrams of laser systems incorporatingdeformable mirrors in accordance with various embodiments of theinvention;

FIGS. 3A and 3B are schematic diagrams of laser systems incorporatinggraded-index lenses in accordance with various embodiments of theinvention;

FIGS. 4A and 4B are schematic diagrams of laser systems incorporatingadjustable lenses in accordance with various embodiments of theinvention;

FIGS. 5A and 5B are schematic diagrams of laser systems incorporatingadjustable end caps in accordance with various embodiments of theinvention;

FIGS. 6A and 6B are schematic diagrams of laser systems incorporatinggraded-index in-coupling fibers in accordance with various embodimentsof the invention;

FIGS. 7A and 7B are schematic diagrams of laser systems incorporatingdeformable mirrors in accordance with various embodiments of theinvention;

FIGS. 8A and 8B are schematic diagrams of laser systems incorporatingdeformable mirrors and multiple input beams in accordance with variousembodiments of the invention;

FIGS. 9A and 9B are schematic diagrams of laser systems incorporatingmultiple input beams with adjustable spacings in accordance with variousembodiments of the invention;

FIG. 9C is a schematic diagram of the input beams at the focusing lensof the laser system of FIG. 9A;

FIG. 9D is a schematic profile of the output beam of the laser system ofFIG. 9A;

FIG. 9E is a schematic diagram of the input beams at the focusing lensof the laser system of FIG. 9B;

FIG. 9F is a schematic profile of the output beam of the laser system ofFIG. 9B;

FIG. 9G is a schematic diagram of a laser system incorporatingredirecting elements in accordance with embodiments of the invention;

FIGS. 9H-9J are schematic diagrams of laser systems incorporatingpathway adjusters in accordance with various embodiments of theinvention;

FIGS. 10A and 10B are schematic diagrams of laser systems incorporatingmultiple variable-power input beams in accordance with variousembodiments of the invention;

FIG. 11A is a schematic diagram of a laser system in which input beamquality is adjusted on the basis of polarization in accordance withvarious embodiments of the invention;

FIG. 11B is a schematic plot of power distribution as a function ofinput numerical aperture for the laser system of FIG. 11A;

FIG. 11C is a schematic diagram of a laser system in which input beamquality is adjusted on the basis of polarization in accordance withvarious embodiments of the invention;

FIG. 11D is a schematic plot of power distribution as a function ofinput numerical aperture for the laser system of FIG. 11C;

FIGS. 11E-11H are schematic diagrams of laser systems in which inputbeam quality is adjusted on the basis of polarization in accordance withvarious embodiments of the invention;

FIGS. 11I and 11J are schematic diagrams of laser systems in which inputbeam quality is adjusted on the basis of polarization and that areutilized with multi-cladding optical fibers in accordance with variousembodiments of the invention;

FIG. 11K is a schematic plot of spatial power distribution within amulti-cladding optical fiber utilized with the laser systems of FIG. 11Ior FIG. 11J; and

FIGS. 12A-12C are schematic diagrams of laser systems in which inputbeam quality is adjusted on the basis of polarization in accordance withvarious embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a laser system 100 in accordance withvarious embodiments of the present invention. In the laser system 100,one or more input beams 105 are focused via a focusing lens 110 into anoptical fiber 115 having a fiber end cap 120. The end cap 120 may be,for example, a piece of “coreless” (i.e., substantially homogeneous) orgraded-index (i.e., having a graded index of refraction) glass, and theend cap 120 may advantageously reduce the optical intensity at theglass-air interface for a given optical power and/or protect the fiber115 from environmental damage (e.g., moisture). As shown, the opticalfiber 115 may have one or more cores 125 surrounded by one or morecladding layers 130. For laser system 100, the BPP of the input beam orbeams 105 is defined as (x/2)×θ=(x×d)/(4×f), where x is the diameter (or“beam size”) of the input beam 105, θ is the laser beam divergence (or“beam divergence”) of the input beam 105, d is the focused diameter ofthe focused input beam 105, and f is the focal length of the focusinglens 110. The beam size is typically calculated in terms of the “secondmoment width” or “D4σ width,” where the D4σ width of a beam in thehorizontal or vertical direction is 4 times σ, where σ is the standarddeviation of the horizontal or vertical marginal distribution,respectively. An optical fiber 110 having a single core 125 and a singlecladding layer 130 may be assumed to have a core diameter of d′ and acladding diameter of D′.

Once the one or more input beams 105 are coupled into the optical fiber115, the fiber 115 outputs an output beam 135. The BPP of the outputbeam 135 (or “output BPP”) may be defined as (d″/2)×NA″, where NA″ isthe numerical aperture of the fiber 115 and d″ is the output beam size.The output beam size d″ depends on the relative amounts of the beampropagating within the cladding 130 and within the core 125 (or,equivalently, the “power content ratio” of the cladding 130 to the core125). For example, the output BPP may be minimized by minimizing theamount of the beam within the cladding 130, and the output BPP may bemaximized by minimizing the amount of the beam within the core 125.Thus, the output BPP may be adjusted to a desired value by focusingdifferent amounts of the input beam(s) within the different regions ofthe fiber 115. In general, the fiber 115 maintains the entry angle (ordivergence or numerical aperture) of input light within the output beam;thus, the output BPP may be advantageously varied via variation of theinput beam quality (or BPP).

Referring to FIGS. 2A and 2B, in an exemplary laser system 200 inaccordance with various embodiments of the present invention, adeformable mirror 210 is utilized to alter the point at which one ormore input beams 105 are focused into the optical fiber 115. As shown inFIG. 2A, in a nominal condition, the input beam(s) 105 are focused bythe deformable mirror 210 and the focusing lens 110 into the core 125 ofthe fiber 115, thus minimizing the output BPP. As shown in FIG. 2B, thedeformable mirror 210 may be manipulated (e.g., by altering the angle ofone or more points on its surface) such that the input beam 105 isfocused such that a fraction of the light spills over into the cladding130, increasing the output BPP. Similarly, the deformable mirror 210 maybe utilized to focus all or part of the focused input beam 105 into acore other than core 125 when the fiber 115 is a multi-core opticalfiber. As known in the art, the deformable mirror 210 may include orconsist essentially of, for example, a segmented mirror formed byindependent flat mirror segments. Each segment may move a small distanceback and forth and/or tilt in one or more directions, in response to anactuator, to alter the wavefront of incoming light. Other exemplarydeformable mirrors 210 include continuous-faceplate mirrors including orconsisting essentially of a continuous membrane deformable by any of anarray of actuators located at the back surface of the membrane.

As shown in FIGS. 2A and 2B, the deformable mirror 210 and/or the arrayof actuators deforming portions thereof are responsive to a controller220, which thereby alters a conformation of the reflective surface ofthe deformable mirror 210. The controller 220 is responsive to a desiredtarget radiation power distribution (e.g., input by a user) andconfigured to produce a mirror conformation causing the input beams tostrike the end face of fiber 115 with the target radiation powerdistribution. The controller 220 may be programmed to achieve thedesired power distribution (and thus the desired output BPP) via aparticular mirror surface conformation without undue experimentation byone of skill in the art. The controller 220 may be provided as eithersoftware, hardware, or some combination thereof. For example, the systemmay be implemented on one or more conventional server-class computers,such as a PC having a CPU board containing one or more processors suchas the Pentium or Celeron family of processors manufactured by IntelCorporation of Santa Clara, Calif., the 680x0 and POWER PC family ofprocessors manufactured by Motorola Corporation of Schaumburg, Ill.,and/or the ATHLON line of processors manufactured by Advanced MicroDevices, Inc., of Sunnyvale, Calif. The processor may also include amain memory unit for storing programs and/or data relating to themethods described above. The memory may include random access memory(RAM), read only memory (ROM), and/or FLASH memory residing on commonlyavailable hardware such as one or more application specific integratedcircuits (ASIC), field programmable gate arrays (FPGA), electricallyerasable programmable read-only memories (EEPROM), programmableread-only memories (PROM), programmable logic devices (PLD), orread-only memory devices (ROM). In some embodiments, the programs may beprovided using external RAM and/or ROM such as optical disks, magneticdisks, as well as other commonly used storage devices. For embodimentsin which the functions are provided as one or more software programs,the programs may be written in any of a number of high level languagessuch as FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scriptinglanguages, and/or HTML. Additionally, the software may be implemented inan assembly language directed to the microprocessor resident on a targetcomputer; for example, the software may be implemented in Intel 80x86assembly language if it is configured to run on an IBM PC or PC clone.The software may be embodied on an article of manufacture including, butnot limited to, a floppy disk, a jump drive, a hard disk, an opticaldisk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gatearray, or CD-ROM.

As shown in FIG. 2C, the deformable mirror 210 may be parabolic (i.e.,have a reflecting surface all or a portion of which is substantiallyparabolic), and such deformable mirrors themselves may focus (evenwithout a separate focusing lens 110) one or more input beams 105 (allor portions of each of which may be manipulated via alterations of thesurface of the deformable mirror 210) to a variety of regions of fiber115, depending upon the desired output BPP of the laser system 200.

Referring to FIGS. 3A and 3B, in an exemplary laser system 300 inaccordance with various embodiments of the present invention, agraded-index (or “GRIN”) lens 310 is utilized to alter the point atwhich one or more input beams 105 are focused into the optical fiber 115and/or the spot size of the focused beam(s). As shown in FIG. 3A, in anominal condition, the input beam(s) 105 are focused by the GRIN lens310 into the core 125 of the fiber 115, thus minimizing the output BPP.In the nominal condition of FIG. 3A, as shown, the input beam(s) 105propagate within the GRIN lens 310 such that the spot size of the inputbeam(s) 105 at the interface between the GRIN lens 310 and the fiber 115is minimized and directed into the core 125. As shown in FIG. 3B, theGRIN lens 310 may be manipulated (or “disturbed” or “perturbed,”indicated by arrows 320) such that the spot size of the input beam(s)105 at the interface between the GRIN lens 310 and the fiber 115 isaltered (e.g., larger). As shown, in the condition depicted in FIG. 3B,a fraction of the incoming light is coupled into the cladding 130 (orinto another core and/or cladding in multiple-core and/ormultiple-cladding fibers), thereby increasing the output BPP. In variousembodiments, when the GRIN lens 310 is disturbed, one or more opticalproperties (e.g., refractive index) change in at least a portion of theGRIN lens 310. For example, the GRIN lens 310 may be disturbed via localheating of a portion of the lens and/or local absorption of radiation ina portion of the lens. In some embodiments, all or a portion of the GRINlens 310 includes or consists of a material exhibiting the acousto-opticeffect, and an acoustic transducer may be utilized to alter the opticalproperties of the GRIN lens 310. For example, the GRIN lens 310 mayinclude or consist essentially of fused silica, lithium niobate, arsenictrisulfide, tellurium dioxide, tellurite glass, lead silicate, and/oranother acousto-optical material. Similarly, an electric field may beapplied to a GRIN lens 310 exhibiting the electro-optic effect to alterits refractive index, thereby disturbing the lens sufficiently to alterthe output BPP.

As shown in FIG. 3B, the means for introducing a distortion in the GRINlens 310 (e.g., at least one of a local heater, a radiation sourcedirected into the lens, an acousto-optic modulator and/or transduceraltering an optical property of the lens, or an electro-optic modulatorand/or transducer altering an optical property of the lens) isresponsive to a controller 220. Controller 220 may be conventional, andmay be configured to introduce and/or control the distortion-inducingmeans in response to a desired output BPP without undue experimentation.

Referring to FIGS. 4A and 4B, in an exemplary laser system 400 inaccordance with various embodiments of the present invention, anadjustable focusing lens 410 is utilized to alter the point at which oneor more input beams 105 are focused into the optical fiber 115 and/orthe spot size of the focused beam(s) via, e.g., manipulation of the lens410 to alter its focal point. As shown in FIG. 4A, in a nominalcondition, the input beam(s) 105 are focused by the adjustable lens 410into the core 125 of the fiber 115, thus minimizing the output BPP. Inthe nominal condition of FIG. 4A, as shown, the input beam(s) 105 arefocused such that the focal point is disposed at the interface betweenthe end cap 120 and the fiber 115; thus, the spot size of the inputbeam(s) is minimized and directed into the core 125. As shown in FIG.4B, the adjustable lens 410 may be manipulated (or “disturbed” or“perturbed”) such that the focal length of the lens 410 changes. Forexample, as shown in FIG. 4B, the focal length may be decreased suchthat the input beams are focused at a point within the bulk of the endcap 120, thereby increasing the spot size at the interface between theend cap 120 and the fiber 115. Thus, in the condition depicted in FIG.4B, a fraction of the incoming light is coupled into the cladding 130(or into another core and/or cladding in multiple-core and/ormultiple-cladding fibers), thereby increasing the output BPP. Theadjustable lens 410 may be perturbed by, e.g., application of heat tothe lens 410 from a heating source 420. As shown, the heating source 420is responsive to a controller 220. Controller 220 may be conventional,and may be configured to introduce heat and/or control the heating levelprovided by the heating source 420 in response to a desired output BPPwithout undue experimentation.

Referring to FIGS. 5A and 5B, in an exemplary laser system 500 inaccordance with various embodiments of the present invention, anadjustable end cap 510 is utilized to alter the point at which one ormore input beams 105 are focused into the optical fiber 115 and/or thespot size of the focused beam(s) via, e.g., manipulation of the end cap510 to alter its optical properties (e.g., refractive index). As shownin FIG. 5A, in a nominal condition, the input beam(s) 105 are focused bya lens (not shown) into the end cap 510 and into the core 125 of thefiber 115, thus minimizing the output BPP. In the nominal condition ofFIG. 5A, as shown, the input beam(s) 105 are focused such that the focalpoint is disposed at the interface between the end cap 120 and the fiber115; thus, the spot size of the input beam(s) is minimized and directedinto the core 125. As shown in FIG. 5B, the adjustable end cap 510 maybe manipulated (or “disturbed” or “perturbed”) such that the focal pointof the input beam(s) changes. For example, as shown in FIG. 5B, thefocal point may be moved to a point within the optical fiber 115,thereby increasing the spot size at the interface between the end cap510 and the fiber 115. Thus, in the condition depicted in FIG. 5B, afraction of the incoming light is coupled into the cladding 130 (or intoanother core and/or cladding in multiple-core and/or multiple-claddingfibers), thereby increasing the output BPP. The adjustable end cap 510may be perturbed by, e.g., application of heat and/or pressure to theend cap 510.

As shown in FIG. 5B, the means 520 for introducing a distortion in thefiber end cap 510 (e.g., at least one of a local heater, a radiationsource directed into the end cap, an acousto-optic modulator and/ortransducer altering an optical property of the end cap, or anelectro-optic modulator and/or transducer altering an optical propertyof the end cap) is responsive to a controller 220. Controller 220 may beconventional, and may be configured to introduce and/or control thedistortion-inducing means in response to a desired output BPP withoutundue experimentation.

Referring to FIGS. 6A and 6B, in an exemplary laser system 600 inaccordance with various embodiments of the present invention, agraded-index (or “gradient-index” or “gradient”) optical fiber isutilized to alter the spot size of the input beam(s) 105 at the inlet ofthe optical fiber 115. As known in the art, a gradient-index fiber is anoptical fiber whose core has a refractive index that decreases withincreasing radial distance from the optical axis of the fiber. Becauseparts of the core closer to the fiber axis have a higher refractiveindex than the parts near the cladding, light rays follow sinusoidalpaths down the gradient-index fiber. The refractive index profile withinthe graded-index fiber 610 may be, for example, substantially parabolic.Thus, the spot size of the beam propagated through the gradient-indexfiber 610 may be controlled via control of the numerical aperture of theinput beam coupled into the gradient-index fiber 610, for example usingone of the numerical-aperture-altering techniques described herein. Asshown in FIG. 6A, one or more input beams 105 having a small numericalaperture (i.e., a small divergence) will propagate through the gradientfiber 610 and produce a small spot size focused such that substantiallyall of the beam is coupled into the core 125 of the fiber 115. As shownin FIG. 6B, one or more input beams 105 having a larger numericalaperture (i.e., a larger divergence) will propagate through the gradientfiber 610 and produce a larger spot size focused such that a portion ofthe beam is coupled into the cladding 130 of the fiber 115, therebyaltering (here increasing) the output BPP. The gradient fiber 610 mayhave a length of, for example, less than approximately 100 mm.

In accordance with various embodiments of the present invention, theoutput BPP of a laser system may be variably controlled via control ofthe input wavefront distribution (i.e., the input beam quality) suchthat at least a portion of the light coupled into an optical fiber isinduced to propagate within one or more cladding layers, rather than thecore of the fiber (and/or within another core of the fiber, for fibershaving multiple cores). For example, FIGS. 7A and 7B depict an exemplarylaser system 700 in accordance with various embodiments of the presentinvention, in which a deformable mirror 210 is utilized to alter thepoint at which one or more input beams 105 is focused into the opticalfiber 115. As shown in FIG. 7A, in a nominal condition, the inputbeam(s) 105 are focused by the deformable mirror 210 and the focusinglens 110 into the core 125 of the fiber 115, thus minimizing the outputBPP. As shown in FIG. 7B, the deformable mirror 210 may be manipulated(e.g., by altering the angle and/or height of one or more points on itssurface) such that phase error is introduced into the input beam 105.The phase error changes the beam quality of the input beam 105, andthus, a fraction of the light spills over into the cladding 130,increasing the output BPP.

As shown in FIGS. 7A and 7B, the deformable mirror 210 and/or the arrayof actuators deforming portions thereof are responsive to a controller220, which thereby alters a conformation of the reflective surface ofthe deformable mirror 210 to introduce phase error into the input beam.The controller 220 may be programmed to achieve the desired phase error(and thus the desired output BPP) via a particular mirror surfaceconformation without undue experimentation by one of skill in the art.

While the laser systems described above (and all laser systems describedherein, unless otherwise indicated) may be utilized with a single inputbeam or multiple input beams, various embodiments of the presentinvention advantageously utilize multiple input beams to controllablyvary the output BPP of the laser system. FIGS. 8A and 8B depict anexemplary laser system 800 in which a deformable mirror 210 is utilizedin conjunction with multiple input beams. FIGS. 8A and 8B depict the useof three input beams 105-1, 105-2, 105-3, but embodiments of theinvention may utilize two input beams or more than three input beams, asdesired. In laser system 800, the deformable mirror 210 is utilized toalter the point at which one or more of the input beams 105 is focusedinto the optical fiber 115. As shown in FIG. 8A, in a nominal condition,the input beams 105-1, 105-2, 105-3 are focused by the deformable mirror210 and the focusing lens 110 to a single focal point and into the core125 of the fiber 115, thus minimizing the output BPP. As shown in FIG.8B, the deformable mirror 210 may be manipulated (e.g., by altering theangle and/or height of one or more points on its surface) such thatphase error is introduced into the input beam 105-3. The phase errorchanges the trajectory of the input beam 105-3 as it propagates to andthrough the focusing lens 110, and thus, the input beam 105-3 is focusedto a point different from the focus point of input beams 105-1, 105-2.Thus, at least a portion of the light of input beam 105-3 enters theoptical fiber 115 at a point different from that where the light frominput beams 105-1, 105-2 enters the fiber, thereby increasing the BPP ofthe combined output beam. For example, as shown in FIG. 8B, the light ofinput beam 105-3 may be focused onto the cladding layer 130 (or one ormore cladding layers, for multi-clad fibers, and/or one or more othercores, for multi-core fibers), while the light of input beams 105-1,105-2 may be focused onto the core 125.

As shown in FIGS. 8A and 8B, the deformable mirror 210 and/or the arrayof actuators deforming portions thereof are responsive to a controller220, which thereby alters a conformation of the reflective surface ofthe deformable mirror 210 to introduce phase error into one or more ofthe input beams. The controller 220 may be programmed to achieve thedesired phase error (and thus the desired output BPP) via a particularmirror surface conformation without undue experimentation by one ofskill in the art.

The beam quality of the input beams may also be changed (therebyenabling controllable variation of output BPP) via alteration of thespacing between the various input beams. FIGS. 9A and 9B depict anexemplary laser system 900 in which the spacing between the input beams105-1, 105-2, 105-3 is varied to change the input beam quality (i.e.,the divergence) coupled into the optical fiber 115. FIG. 9A depicts theinput beams 105-1, 105-2, 105-3 being separated by a relatively narrowspacing 910-1, which results in the input beams being focused into thefiber 115 by focusing lens 110 with a relatively small divergence angle920-1. The relatively small entrance angle into the fiber 115 results ina smaller output BPP. FIG. 9B depicts the input beams 105-1, 105-2,105-3 being separated by a spacing 910-2 larger than the spacing 910-1,which results in the input beams being focused into the fiber 115 byfocusing lens 110 with a divergence angle 920-2 larger than divergenceangle 920-1. The larger entrance angle into the fiber 115 results in alarger output BPP. In this manner, the output BPP of laser system 900may be varied by varying the spacing between the input beams coupledinto the fiber 115. In general, the spacing between the input beams maybe varied such that the divergence angle of the focused beams enteringthe fiber does not exceed the acceptance angle of fiber 115. In variousembodiments, the acceptance angle θ_(accept) of fiber 115 may becalculated by the equation: n sin θ_(accept)=√{square root over(n_(core) ²−n_(clad) ²)}, where n is the index of refraction of themedium from which the light beam is entering the fiber (for example, theindex of refraction of air or of the end cap 120), n_(core) is the indexof refraction of the core (or of the central optical axis) of the fiber,and n_(clad) is the index of refraction of the cladding of the fiber.

FIG. 9C is a schematic diagram of the three input beams at the focusinglens of the laser system 900 of FIG. 9A, in which the input beams 105-1,105-2, 105-3 are initially separated by a smaller spacing 910-1. Asshown, upon entry into the fiber 115, the three input beams arerelatively closely spaced together, reducing (or even minimizing) theoutput BPP of the laser system. FIG. 9D shows one exemplary profile ofan output beam of the laser system 900 of FIG. 9A.

In contrast, FIG. 9E is a schematic diagram of the three input beams atthe focusing lens of the laser system 900 of FIG. 9B, in which the inputbeams 105-1, 105-2, 105-3 are initially separated by the larger spacing910-2. As shown, upon entry into the fiber 115, the three input beamsare relatively farther apart, increasing the output BPP of the lasersystem. FIG. 9F shows an exemplary profile of an output beam of thelaser system 900 of FIG. 9B.

FIG. 9G schematically depicts an exemplary technique for varying thespacing of the input beams of laser system 900. In FIG. 9G, multipleindividual emitters 930 each emit an input beam 105, and the input beams105 are initially propagating with a spacing 940 therebetween. The inputbeams 105 are redirected by one or more redirecting elements (e.g.,mirrors, lenses, etc.) 950 such that, after redirection, the input beams105 are spaced at a spacing 910 different from (and in FIG. 9G, smallerthan) spacing 940. The redirecting elements 950 may be individually orcollectively translated and/or rotated to produce a desired spacing 910between two or more of the input beams 105. As detailed above, thespacing 910 results in an entry angle 920 that directly impacts theoutput BPP of the laser system 900. The redirecting elements 950 may beindividual discrete elements, or they may be individual portions orsegments of a larger redirecting element such as a mirror (e.g., adeformable mirror) or a lens. In addition, while the input beams 105 areshown as substantially parallel before and after redirection byredirection elements 950, in various embodiments of the invention, thepropagation angle between the input beams may also be varied, therebyvarying the points at which the individual beams strike the focusinglens 910 for focusing toward the fiber 115. As shown in FIG. 8B, sucharrangements may enable the selective focusing of one or more inputbeams (or portions thereof) onto different regions of the fiber 115(e.g., one or more cladding layers and/or one or more cores).

As shown in FIGS. 9H and 9I, the entry angle of the input beams into theoptical fiber may be varied even when the spacing between the inputbeams is substantially unchanged. As shown, a pathway adjuster 960 maybe utilized to adjust the propagation path of one or more input beams105. The pathway adjuster 960 may include or consist essentially of, forexample, a prism, a grating, a lens, etc. Although the pathway adjuster960 is depicted in FIGS. 9H and 9I as a single object, in variousembodiments the pathway adjuster 960 includes or consists essentially ofa collection of individually controllable (e.g., rotatable and/ortranslatable) pathway adjusters each receiving one or more input beams(as shown, e.g., in FIG. 9J). As shown in FIG. 9H, in a nominal case,the pathway adjuster 960 does not alter the propagation path of theinput beams 105, which are subsequently focused by lens 110 into thefiber 115 with an entry angle 920-3. In FIG. 9I, the pathway adjuster960 is rotated such that, when the input beams 105 pass through thepathway adjuster 960, they propagate along a path 970 within the pathwayadjuster 960 and exit the pathway adjuster 960 having had theirpropagation path altered. As shown, the input beams 105 subsequentlystrike the focusing lens 110 in different spatial locations, resultinginto their in-coupling into the optical fiber 115 with an entry angle920-4 different from angle 920-3, thereby altering the output BPP of thelaser system 900.

FIG. 9J depicts an exemplary laser system 900 in which the spacingbetween input beams and the propagation path of individual input beamsmay both be varied. As shown, each input beam 105 may have itspropagation path adjusted by a pathway adjuster 960, thereby changingthe spacing between various input beams 105 and/or the locations atwhich the input beams strike the focusing lens 110 for focusing into theoptical fiber 115. In the example shown in FIG. 9J, input beams 105having their paths adjusted appear as dashed lines, while unadjustedinput beams 105 appear as solid lines. Once the input beams 105 strikethe focusing lens 110, they are focused into the fiber 115 with an entryangle 920-5 that may vary depending on which (and/or how many) inputbeams have their paths adjusted and/or to what extent they are adjusted.

The beam quality (and thus BPP) of the output beam of laser systems inaccordance with embodiments of the present invention may also becontrollably varied by adjusting the power characteristic of one or moreof the input beams (which, in turn, impacts the beam quality of theinput beam in-coupled into the optical fiber). FIG. 10A depicts anexemplary laser system 1000 in accordance with embodiments of theinvention that resembles laser system 900 of FIG. 9B. As shown, theinput beams 105-1, 105-2, 105-3 are spaced apart at a particular spacingand focused into the fiber 115 via focusing lens 110. In FIG. 10B, thepower characteristic (e.g., output power) of the input beam 105-3 hasbeen reduced, reducing its contribution to the combined beam in-coupledinto the fiber 115. This alters the beam quality (and thus the outputBPP) of the resulting output beam emitted at the other end of fiber 115.In some embodiments, one or more of the input beams is varied in outputpower, or even shut off entirely, resulting in changes in the in-coupledbeam quality and thus the output BPP of the laser system.

The power characteristic of the input beams may be controlled by acontroller 220 that controls the various emitters of each of the inputbeams. The controller 220 may be programmed to achieve the desired beamconformation (and thus the desired output BPP) via power modulation ofone or more of the input beams without undue experimentation by one ofskill in the art.

In various embodiments of the present invention, input beam quality isvaried (leading to variation in output BPP) on the basis of thepolarization state of the input beams. Specifically, input beams may beseparated into components having different polarization states andrecombined into input beams having desired power levels. Then, one ormore of the recombined beams may be focused onto one region of theoptical fiber (e.g., the core) while one or more other recombined beamsmay be focused onto a different region of the optical fiber (e.g., thecladding), resulting in an output beam having a BPP adjustable on thebasis of the ratio of power levels of the two recombined beams. FIG. 11Adepicts an exemplary laser system 1100 in which two linearly polarizedinput beams 105-1, 105-2 are manipulated on the basis of polarization.As shown, the two input beams pass through a half-wave plate 1105, whichalters the polarization direction of the light of the input beams.Specifically, rotation of the half-wave plate 1105 allocates the powerof each of the input beams into one of two different polarizationstates, e.g., s-polarized (or simply “S”) and p-polarized (or simply“P). As known in the art, p-polarized light has its electric field alongthe plane of incidence (i.e., the plane made by the propagationdirection and a vector perpendicular to the plane of a reflectingsurface), while s-polarized light has its electric field normal to theplane of incidence. The half-wave plate 1105 typically includes orconsists essentially of a birefringent material (such as quartz ormica), the index of refraction of which is different for differentorientations of light passing through it. After passing through thehalf-wave plate 1105, the input beams are split into S and P componentsby a polarizer beam splitter 1110 (e.g., a thin-film polarizer or aWollaston prism), components the relative power of which was selected bythe rotation of the half-wave plate 1105. (Note that S and P aredesignations for any two polarization states that are selectable in thismanner.) As shown, the P light passes straight through the polarizerbeam splitter 1110, while the S light is split away and directed towarda reflector 1115. Both S and P light are then directed to the focusinglens 110 for focusing into the optical fiber (the optical fiber 115 isnot depicted in FIG. 11A and subsequent figures for clarity). The Plight may be focused into the optical fiber (e.g., into its core) with asmall numerical aperture (or divergence or entry angle) 1120, while theS light, spatially separated from the P light, may be focused into theoptical fiber (e.g., into its cladding) with a larger numerical aperture1125. In this manner, the contributions of the S and P light to thecombined output beam (and thus its BPP) may be varied simply byallocating power to the input beams via the half-wave plate 1105. Insome embodiments, the S light is focused onto the fiber core while the Plight is focused onto the fiber cladding. In other embodiments, afterthe input beams have been separated on the basis of polarization, andtheir relative powers allocated via half-wave plate 1105, the S and Plight may be directed through a polarization scrambler 1130 thatdepolarizes the different light beams (e.g., imparts the beams withrandom polarizations or with both S and P polarizations) before they arefocused into different locations of the fiber. The polarizationscrambler may include or consist essentially of, for example, aquarter-wave plate. FIG. 11B depicts a schematic plot of the input-beampower within the numerical apertures 1120, 1125 for the laser system1100 of FIG. 11A.

Although the laser system 1100 of FIG. 11A separates input beams, bypolarization state, into beams that are in-coupled into an optical fibersubstantially free of spatial overlap, the beams may also be partiallyoverlapped, as shown in FIG. 11C. In FIG. 11C, the power of the inputbeams 105-1, 105-2 is again allocated between S and P polarizations viaa desired rotation of the half-wave plate 1105, and the resulting beamsare split into S and P components by a beam displacer 1135. The beamdisplacer 1135, which in general splits unpolarized light into polarizedbeams having orthogonal polarizations and propagating at differentangles, may include or consist essentially of a uniaxial crystal of amaterial such as yttrium vanadate (YVO₄), barium borate (α-BBO), calcitecrystal, or rutile. The S and P components of the input beams arefocused by the focusing lens 110 onto different but overlapping regionsof the optical fiber, where the S light is focused into the opticalfiber (e.g., into its core) with a small numerical aperture (ordivergence or entry angle) 1120, while the P light is focused into theoptical fiber (e.g., into the cladding and a portion of the core) with alarger numerical aperture 1125, with the P light overlapping the S lightupon entry into the fiber. FIG. 11D schematically depicts the powerdistribution between the numerical apertures 1120, 1125, showing theoverlap between the two beam components. As in laser system 1100 of FIG.11A, the output BPP may be variably selected via the relative allocationof the input beam power into S and P components by the half-wave plate1105.

FIG. 11E depicts an exemplary laser system 1100 in accordance withembodiments of the present invention in which up to 50% of the totalpower of the input beams 105-1, 105-2 may be allocated to the largernumerical aperture 1125 of the optical fiber, the remaining portionbeing allocated to the smaller numerical aperture 1120. In FIG. 11E, theinput beams 105-1, 105-2 are initially randomly polarized and/or arepassed through an optional polarization randomizer 1140 (e.g., aquarter-wave plate). As in FIG. 11A, the input beams are then split bypolarization beam splitter 1110 into S and P components, and the Scomponents are directed toward reflector 1115. The reflected Scomponents are then repolarized into light beams having both S and Ppolarizations by a half-wave plate 1145, which is rotated to select therelative amount of S and P polarization in the resulting light beams.The repolarized light beams are directed to a second polarization beamsplitter 1150, which passes the P components of the light beams to thefocusing lens 110 for focusing into the larger numerical aperture 1125.In this manner, up to 50% of the power of the original input beams150-1, 150-2 (i.e., up to 100% of the power initially split into Spolarization by the polarization beam splitter 1110) may be allocated tothe larger numerical aperture 1125. The S light from the half-wave plate1145 is directed from polarization beam splitter 1150 to anotherpolarization beam splitter 1155, where it is recombined with the P lightexiting the initial polarization beam splitter 1110. As shown, thatcombined light is focused into the smaller numerical aperture 1120.

Similarly to FIG. 11C, a laser system 1100 having randomly polarizedinput beams may also allocate light power between two numericalapertures with overlap of the light. FIG. 11F depicts such an exemplarylaser system 1100, in which the input beams 105-1, 105-2 are initiallyrandomly polarized and/or are passed through an optional polarizationrandomizer 1140 (e.g., a quarter-wave plate). As in FIG. 11C, the beamsare directed to beam displacer 1135, which splits the input beams into Sand P components. These components pass through a half-wave plate 1160and then propagate to a beam combiner 1165. The beam combiner 1165,which typically includes or consists essentially of the same opticalcomponent as beam displacer 1135, only utilized in the opposite manner,recombines S and P components at its output. As shown, rotation of thehalf-wave plate 1160 allocates the initial power of input beams 105-1,105-2 in full or in part to each of the smaller numerical aperture 1120and the larger numerical aperture 1125 (once the light is focused by thefocusing lens 110).

FIGS. 11G and 11H schematically depict the two extreme cases of thelaser system 1100 depicted in FIG. 11F. In FIG. 11G, the half-wave plate1160 is rotated at, for example, 0 degrees or 90 degrees, and thus allof the initial power of the input beams 105-1, 105-2 is allocated to thesmaller numerical aperture 1120. In FIG. 11H, the half-wave plate 1160is rotated at, for example, 45 degrees, and thus all of the initialpower of the input beams 105-1, 105-2 is allocated to the largernumerical aperture 1125.

In accordance with various embodiments of the present invention,input-beam light may be separated on the basis of polarization for powerallocation among different cladding layers of a multi-cladding opticalfiber. FIG. 11I depicts an exemplary laser system 1100 similar to thatof FIG. 11A, except that the reflector 1115 is tilted so that theseparated S and P components propagate toward the focusing lens 110 at anon-zero angle 1170 therebetween (rather than propagating parallel toeach other). As described above, rotation of the half-wave plate 1105allocates the total power of the input beams 105-1, 105-2 between thetwo polarization states, one of which is focused to a point 1175 (e.g.,to the core of the optical fiber), and the other of which (due to theangle 1170) is focused to a point 1180 different than point 1175 (e.g.,to a cladding layer, for example an outer cladding layer surrounding aninner cladding layer, of the optical fiber). Similarly, FIG. 11J depictsan exemplary laser system 1100 similar to that of FIG. 11C, except thata surface 1185 of the beam displacer is cut at an angle (or “wedged”) sothat the separated S and P components propagate toward the focusing lens110 at a non-zero angle 1170 therebetween (rather than propagatingparallel to each other). As described above, rotation of the half-waveplate 1105 allocates the total power of the input beams 105-1, 105-2between the two polarization states, one of which is focused to a point1175 (e.g., to the core of the optical fiber), and the other of which(due to the angle 1170) is focused to a point 1180 different from point1175. FIG. 11K depicts an exemplary plot of power distribution in thespatial domain within the fiber 115 for the laser systems 1100 depictedin FIGS. 11I and 11J. As shown, the light directed to point 1175 isin-coupled into the core 125 of the fiber, while the light directed topoint 1180 is coupled into a second cladding layer 130-2 that surroundsa first cladding layer 130-1. In other embodiments, light directed topoint 1180 may be coupled into a second core or a different cladding ofa multi-core/multi-cladding fiber. While these examples are variants ofthe laser systems of FIGS. 11A and 11C utilizing linearly polarizedinput light, the same principle may be applied to the systems of FIGS.11E and 11F utilizing randomly polarized input light.

FIG. 12A depicts an exemplary laser system 1200 that is functionallysimilar to the laser system 1100 depicted in FIG. 11E, in that therotation of half-wave plate 1145 allocates the total power of inputbeams 105-1, 105-2 fully or partially to a smaller numerical aperture1120 or to a larger numerical aperture 1125. In the laser system 1200 ofFIG. 12A, the input beams, which may either be randomly polarized orinitially pass through a polarization randomizer such as a quarter-waveplate (not shown) propagate to a substantially optically transparentplate 1205 having a polarization beam splitting surface 1210 and ahighly reflective surface 1215. As shown, the polarization beamsplitting surface 1210 splits the input beams into S and P components,the S component reflecting from the polarization beam splitting surface1210 toward half-wave plate 1145 and the P component propagating throughthe plate 1205 and being reflected toward half-wave plate 1145 byreflective surface 1215. As described herein, rotation of the half-waveplate 1145 allocates the total power to the S and P components, whichthen propagate to a second substantially optically transparent plate1220 having a polarization beam splitting surface 1225 and a highlyreflective surface 1230. As shown, the plate 1220 (and/or its reflectiveand/or polarization beam splitting surfaces) is generally parallel tothe plate 1205 (and/or its reflective and/or polarization beam splittingsurfaces). The interaction of the light with the surfaces 1225, 1230 ofplate 1220 redistributes the light, allocated via half-wave plate 1145,into components focused by focusing lens 110 into the smaller numericalaperture 1120 and the larger numerical aperture 1125.

FIG. 12B depicts an exemplary laser system 1200 in accordance withembodiments of the invention that is similar to the laser system 1200 ofFIG. 12A. In the laser system 1200 of FIG. 12B, the substantiallyoptically transparent plates 1205, 1220 (and/or their reflective and/orpolarization beam splitting surfaces) are arranged at opposite angles,i.e., angles the same rotational distance from zero degrees but inopposite directions. Such arrangements may result in the plates beingmore easily configured with respect to each other, and the lightentering the focusing lens 110 propagates generally along the same pathas that of the original input beams 105-1, 105-2. As in laser system1200 of FIG. 12A, the input beams 105-1, 105-2 propagate to the plate1205, split into S and P components and reflect toward the half-waveplate 1145. Rotation of the half-wave plate 1145 allocates power betweenthe S and P components, which are then reflected toward plate 1225 by areflector 1235. As in laser system 1200 of FIG. 12A, the allocated beamsare focused by focusing lens 110 into the smaller numerical aperture1120 and the larger numerical aperture 1125.

FIG. 12C depicts a similar laser system 1200 in accordance with variousembodiments of the invention. As shown, the input beam 105 is directedtoward plate 1205, split into S and P components, which are reflected toa reflector 1240 and thence to the half-wave plate 1145. Rotation of thehalf-wave plate 1145 allocates power between the S and P components,which are then reflected toward plate 1225 by a reflector 1245. In thelaser system 1200 of FIG. 12C, the plates 1205, 1220 and/or thereflectors 1240, 1245 are disposed at opposite angles. As in lasersystem 1200 of FIG. 12A, the allocated beams are focused by focusinglens 110 into the smaller numerical aperture 1120 and the largernumerical aperture 1125.

The terms and expressions employed herein are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:
 1. A beam-parameter adjustment system and focusingsystem for receiving and altering a spatial distribution of a pluralityof radiation beams from a plurality of beam sources and focusing theradiation with the altered spatial distribution onto an end face of anoptical fiber, the radiation beams each having a polarization state andcollectively having a spatial distribution, the system comprising: afirst optical element for splitting each of the radiation beams into aplurality of spatially displaced output beams, the splitting being basedon the polarization states; focusing optics for combining the outputbeams onto the optical-fiber end face; and a second optical element foraltering a polarization state of (i) at least one of the radiation beamsand/or (ii) at least one of each plurality of output beams prior tocombination thereof by the focusing optics, whereby the combined outputbeams have an output spatial distribution different from the spatialdistribution of the radiation beams, the output distribution beingdetermined by the polarization-based splitting.
 2. The system of claim1, wherein the second optical element is a half-wave plate.
 3. Thesystem of claim 2, wherein the first optical element is a polarizingbeam splitter for splitting the radiation beams into the output beams inaccordance with the polarization states of the radiation beams.
 4. Thesystem of claim 2, wherein the half-wave plate is optically upstream ofthe polarizing beam splitter.
 5. The system of claim 3, furthercomprising a polarization randomizer, optically upstream of the focusingoptics, for randomizing polarization states of the output beams.
 6. Thesystem of claim 5, wherein the polarization randomizer is a quarter-waveplate.
 7. The system of claim 5, wherein the polarization randomizer isa polarization scrambler.
 8. The system of claim 2, wherein the firstoptical element is a birefringent beam displacer for spatiallydisplacing at least some of the radiation beams based on thepolarization states thereof.
 9. The system of claim 8, wherein the beamdisplacer is uniaxially birefringent, whereby each of the radiationbeams is split into an ordinary beam propagating along an optical axisof the beam displacer and an extraordinary beam propagating away fromthe optical axis.
 10. The system of claim 9, wherein a powerdistribution between each of the ordinary and extraordinary beamsdepends on polarization components of the corresponding radiation beam.11. The system of claim 1, wherein the first optical element comprisesfirst and second polarizing beam splitters and the second opticalelement comprises a half-wave plate disposed between the first andsecond polarizing beam splitters along an optical axis thereof, wherein(i) the first polarizing beam splitter splits the radiation beams into aplurality of spatially displaced intermediate beams in accordance withthe polarization states of the radiation beams, some but not all of theintermediate beams propagating along the optical paths of the radiationbeams and some of the intermediate beams propagating parallel to butspatially displaced from the optical paths of the radiation beams, (ii)the second optical element intercepts and alters polarization states ofat least some of the displaced intermediate beams, and (iii) the secondpolarizing beam splitter combines at least some of the displacedintermediate beams with the intermediate beams that have not beendisplaced based on the altered polarization states of the displacedintermediate beams intercepted by the second optical element.
 12. Thesystem of claim 11, further comprising a quarter-wave plate, opticallyupstream of the first polarizing beam splitter, for establishing thepolarization states of the radiation beams.
 13. The system of claim 1,wherein the first optical element comprises first and secondbirefringent beam displacers and the second optical element comprises ahalf-wave plate disposed between the first and second beam displacersalong an optical axis thereof, wherein (i) the first beam displacerdisplaces each of the radiation beams into an ordinary intermediate beampropagating along an optical axis of the beam displacer and anextraordinary intermediate beam propagating away from the optical axisbased on the polarization states of the radiation beams, (ii) the secondoptical element intercepts and alters polarization states of theintermediate beams, and (iii) the second beam displacer displaces theintermediate beams based on the altered polarization states thereof. 14.The system of claim 13, wherein further comprising a quarter-wave plate,optically upstream of the first polarizing beam splitter, forestablishing the polarization states of the radiation beams.
 15. Thesystem of claim 12, wherein a rotation angle of the half-wave plateabout an optical axis thereof determines an allocation of beam powerbetween a maximum numerical aperture of the radiation beams and aminimum numerical aperture of the radiation beams.
 16. The system ofclaim 3, wherein the polarizing beam splitter has a top reflectivesurface angled so that the output beams propagate at an off-parallelangle relative to optical paths of the radiation beams.
 17. The systemof claim 8, wherein the beam displacer is wedged so that the outputbeams propagate at an off-parallel angle relative to optical paths ofthe radiation beams.
 18. The system of claim 1, wherein the firstoptical element comprises first and second spaced-apart, substantiallyoptically transparent plates oriented parallel to each other but angledwith respect to optical paths of the radiation beams and the secondoptical element is a half-wave plate intervening between the first andsecond plates, each of the first and second plates having a birefringentsurface facing the second optical element and a highly reflectivesurface opposite the birefringent surface.
 19. The system of claim 18,wherein a rotation angle of the half-wave plate about an optical axisthereof determines an allocation of beam power between a maximumnumerical aperture of the radiation beams and a minimum numericalaperture of the radiation beams.
 20. The system of claim 1, wherein thefirst optical element comprises at least one reflector and first andsecond spaced-apart, substantially optically transparent plates orientedat opposite angles with respect to optical paths of the radiation beamsand the second optical element is a half-wave plate, each of the firstand second plates having a birefringent surface facing the secondoptical element and a highly reflective surface opposite thebirefringent surface.
 21. The system of claim 20, wherein the first andsecond plates are disposed along the optical paths of the radiationbeams, the reflector is spaced apart from the optical paths of theradiation beams, and the half-wave plate is disposed between the firstplate and the reflector, the first and second optical elements beingarranged such that intermediate beams from the first plate travelthrough the half-wave plate and are reflected by the reflector to thesecond plate from which they propagate through the focusing optics. 22.The system of claim 20, wherein the first and second plates are disposedalong the optical paths of the radiation beams, first and secondreflectors are spaced apart from the optical paths of the radiationbeams and oriented at opposite angles with respect to each other, andthe half-wave plate is disposed between the reflectors, the first andsecond optical elements being arranged such that intermediate beams fromthe first plate are directed through the half-wave plate by the firstreflector and to the second plate by the second reflector so as topropagate through the focusing optics.